The present invention is directed to a) a method of enhancing the magnetic susceptibility of plastic material to enable it to be recycled, b) the plastic with enhanced susceptibility and c) a method of separating the susceptible plastic from a waste stream.
Plastics have found wide acceptance in industry and are used to make many articles that have a variety of applications. Hundreds of types of plastics are routinely used for commercial and consumer products such as containers for household cleaners and detergents, industrial chemicals, automobile components, children's toys and various other consumer goods. With the exception of a small percentage of household consumer products, a great majority of plastic polymers are simply discarded due to a lack of acceptable recycling techniques. Unfortunately, disposal of these plastics contributes to a continuous accumulation of consumer refuse and represents a vast waste of natural resources. The growing stacks of plastic articles at waste disposal facilities are monuments being built to our failure to effectively recycle these plastics.
Considerable research has been conducted over the past several decades with regard to material recycling. Industrial materials such as rubber tires, chopped wire and cable, and various metals from automobile shredding are currently reclaimed with commercial success using different physical processing techniques. For example, rubber tires are currently shredded/granulated to liberate nylon cord and metal belting. The nylon and metal are subsequently removed using a combination of screening, air classification and magnetic separation. The final granulated rubber product has sufficient purity to be recycled into various components such as paving materials and play area ground coverings.
Wire and cable are also extensively recycled with the intent to recover both the copper and/or aluminum wire and the plastic insulation. A typical communications cable consists of approximately 80-85% copper and various types of plastics. The cable is typically sheared into smaller pieces suitable for shredding/granulation. The granulated product (particle size of approximately 6 mm and smaller) is air-classified to remove dust/fluff and separated into metallic (copper/aluminum) and non-metallic (plastic) components using gravity and electrostatic-based separation procedures. This approach produces a high-quality metal product that can be sold directly as a commodity.
Unfortunately, the plastic by-product from this approach is often not of an acceptable quality for re-use since it consists of a mixture of components such as PVC, PET, rubber and other plastics. Each plastic component must be refined to an acceptable quality to be considered for recycling by mixing with virgin components. Further refining of the different plastic components, however, has proven a difficult task.
Various attempts have been made to recycle mixed plastic components. These have included gravity and electrostatic separation. Gravity-based processes rely upon the density difference between plastic components. For instance, process specifications may require separation of two components having a density difference of less than 0.05 specific gravity units. Separation of components with nearly the same density requires an extremely precise process that, while possible, is not practical in a continuous commercial process. Furthermore, control of media density at such a low value requires the use of dissolved salts. This presents two additional problems: high corrosion of process equipment and the need to rinse and dry the final products (which adds cost).
Another attempt to separate plastics employs electrostatic techniques. Triboelectrostatic separation depends upon the electrical properties of the plastic surface. Specifically, the work function of one plastic must differ substantially from the second plastic component so as to acquire an opposite electrical charge. Unfortunately, this approach suffers from an extremely low throughput capacity and an inability to produce a high purity product. Additionally, since the separation mechanism is surface dependent, coatings, contaminants and changes in atmospheric conditions (i.e., temperature and humidity) can affect the quality of the separation. Gravity- and electrostatic-based processes have had limited success since these techniques cannot achieve the desired product purity at an acceptable product recovery rate.
Limited success has also been achieved in recycling of post consumer waste. In this instance, plastics are hand sorted from other refuse by consumers and disposed of using curbside collection facilities. Separation of the various types of plastics (i.e., PVC, PET, etc.) Is accomplished by hand sorting at material recycling facilities. In some instances, whole bottle sorting machines have been employed in place of hand sorting.
It is apparent that the current methods for recycling plastic are woefully inadequate to accomplish efficient separation of high purity plastics of the type needed for most recycling applications. Accordingly, it is the intention of the present invention to suggest a different approach that is capable of providing a high-purity recycled plastic product at acceptable processing rates.
In order to produce an effective separation process, it was necessary to re-engineer the plastic to be separated. That is, it is a distinctive feature of the present invention to manipulate the magnetic susceptibility of plastic polymers used to formulate products through the use of additives. It is well known that magnetic separation is an efficient, high capacity process that is well suited for separation of granular-size material. The concept of magnetic separation is based on the ability to attract a particular material exhibiting a magnetic susceptibility and then physically segregate it from particles that are non-magnetic or that have a different susceptibility. Magnetic susceptibility is an inherent property of a material and, as such, is the single most important parameter when addressing the characteristics of magnetic separation. Unfortunately, plastic polymers do not exhibit a natural magnetic susceptibility of sufficient magnitude to permit separation.
In the present invention, the magnetic susceptibility of a plastic polymer is altered by the inclusion of a ferromagnetic material, selected from the group consisting of magnetite (Fe3O4), ferro-silicon, and ferrous metal particles (e.g., iron filings), in the formulation prior to the product's formation (although it will be appreciated other ferromagnetic materials could be used to alter the material's magnetic susceptibility).
The present invention comprises a method of enhancing the magnetic susceptibility of a plastic article to facilitate its removal from other material for recycling, by blending a given amount of a magnetic material into a plastic formulation prior to formation of said article, the given amount being small enough so as not to materially affect properties associated with its function while being large enough to alter the magnetic susceptibility of the article. The magnetic material is preferably selected from a group consisting of magnetite and ferrous metal particles which is/are added in a range between 0.01% and 5% by weight.
Another facet of the present invention is a plastic material with enhanced magnetic susceptibility facilitating its removal from other material to permit its recycling, the plastic material comprising a plastic polymer into which is blended a given amount of a magnetic material prior to formation of an article, the given amount being small enough so as not to materially affect properties associated with the function of the article while being large enough to alter said magnetic susceptibility of the article.
The invention further includes a process for separating at least one plastic polymer having enhanced magnetic susceptibility from a stream of articles, the stream including plastic articles, the method comprising at least two of the steps of a) reducing a size of the plastic articles into a range of sizes of plastic particles; b) classifying the range of sizes of plastic particles; c) preparing the classified plastic particles; d) removing tramp metal from the prepared plastic particles; and e) subjecting the prepared plastic particles to at least a first magnetic field to remove the plastic polymer having enhanced magnetic susceptibility from the prepared plastic particles. Preferably, the process of claim 7 wherein said at least two steps include steps a) and e).
The separating process preferably comprises subjecting the prepared plastic particles to at least one additional magnetic field having a different strength than the first magnetic field to remove at least one additional polymer with a different level of enhanced magnetic susceptibility than the first plastic polymer. The reducing step comprises performing a function selected from the group consisting of crushing, shredding, grinding and granulating and the classifying step comprises performing at least one of the functions selected from the group consisting of de-dusting and screening. The preparing step comprises performing at least one operation selected from the group consisting of drying and cleansing a surface of the classified particles. The invention may include performing a step of secondary separation of the removed plastic polymer.
Various other features, advantages and characteristics of the present invention will become apparent to one of ordinary skill in the art after a reading of the following specification.